Changes in aquatic vegetation communities based on satellite images before and after pen aquaculture removal in East Lake Taihu

Abstract

为削减东太湖养殖污染，改善湖泊水质，苏州市于2018年底基本完成东太湖养殖围网拆除工作.围网拆除后，湖泊生态环境对此如何响应，已成为学者及相关管理部门关注的重点.水生植被在维持湖泊生态系统平衡、物质循环和净化水质方面发挥着重要的作用，是诊断湖泊生态系统健康状态的关键指标.本研究基于Sentinel-2卫星数据，利用分类决策树模型和基于生活史的沉水植被优势种群提取方法，监测了东太湖2017年（围网拆除前）和2019年（围网拆除后）的水生植被类群和沉水植被优势种群的空间分布.经验证，水生植被类群监测精度为82.66%，Kappa系数为0.77；沉水植被优势种群的监测精度为62.08%，Kappa系数为0.56.结果表明：围网拆除后，东太湖水生植被优势类群由围网拆除前的沉水植被转变为浮叶植被；沉水植被分布面积减少，且种群由优势度相差不大的七大优势种群逐步向菹草和伊乐藻占据绝对优势发展，逐渐趋于单一化.;To improve water quality and enhance ecological management, all the net-pen aquaculture facilities in the East Lake Taihu have been removed by the end of 2018. Understanding the impact of this activity on lake ecosystem health is critical to promote efficient ecological management. Aquatic vegetation, especially submerged aquatic vegetation is an essential component of healthy lake ecosystem, as they provide food and shelter, help to secure and stabilize shorelines and modulate nutrient circulation. Additionally, submerged aquatic vegetation can improve water clarity by competing for nutrient with algae. Monitoring submerged aquatic vegetation is fundamental to lake ecosystem health evaluation. In this study, we leverage Sentinel-2 data to map the temporal change of different types of aquatic vegetation types (i.e., emergent vegetation, floating-leaved vegetation and submerged aquatic vegetation), as well as the dominant submerged aquatic vegetation species. We found that the dominant vegetation shifted from submerged to floating-leaved vegetation after the pen aquaculture removal in East Lake Taihu. Meanwhile, the total coverage of submerged aquatic vegetation and its diversity significantly decreased, suggesting environmental degradation in this area. Our research indicated that removing net-pen culture has negative effect on lake ecosystem health. Efficient ecological management of this critical lake system requires comprehensive evaluation before they implement any management activities.